DESCRIPTION: (Adapted from Applicant's Description) During the initial funding period of this RFA, the investigators determined that the expression of the anti-adhesive molecule, polymorphic epithelial mucin (Muc-1) on the baboon uterine surface epithelium is associated with the pre-receptive stage (days 5-8 post-ovulation [PO]). With the onset of uterine receptivity (days 8-10 PO), Muc-1 and the progesterone receptor decrease and smooth muscle myosin II (SMM II) and the ultrastructural apical marker known as "pinopods" appear on the surface epithelium. Glandular epithelial expression of the integrins alpha1 and alpha4 is also evident. The post-receptive phase (day 12 PO onwards) is characterized by the glandular expression of placental protein 14 (PP14). The investigators now propose to extend their studies to the second phase of uterine receptivity. This phase is characterized by the influence of a preimplantation embryo or a blastocyst "signal" on the hormonally primed receptive endometrium. The specific aims of this application are to determine: 1) the effect of chorionic gonadotrophin (CG) infusion in modulating the uterine environment between days 8 and 12 PO; 2) the role of progesterone and estrogen in enhancing endometrial receptivity in response to blastocyst signalling; and 3) the effects of ovarian hyperstimulation on uterine receptivity. The first two specific aims will utilize the baboon as a non-human primate model and the third specific aim will focus on women enrolled in an oocyte donor program.